1. Field of Invention
This invention relates to drive trains and more particularly to drive trains provided with a means for preventing the transmission of motion in the reverse direction.
2. Prior Art
With reference to gear trains utilized in time keeping devices, the motion under ordinary conditions is transmitted from the drive member such as a balance compensating motor, tuning fork motor, stepping motor, etc., to a side where the time in indicated by long and short hand. However, in adjusting the hands to set the time, motion is often transmitted from the indication side to the drive member. Motion transmitted in a reverse direction often causes changes in the state of the drive member, often causing the time keeping device to be out of order even when the device is set to work properly. For example, the hands being adjusted transmit motion reversely in the train of gears. When this motion is transmitted reversely in the train of gears and if the rotor of a stepping motor is turned by this transmitter reverse motion, the rotor will not rotate a full step when the initial pulse is applied.
To prevent the occurance of such an undesirable event, the prior art time keeping devices are equiped with a slip mechanism at the indication part or between the indication part and the drive train and a stop mechanism in the train of gears to prevent the transmission of reverse motion in the gear train. In many cases, the slip mechanism may consist of compressing some part of the cannon pinion and pressing the inner surface thereof into the outer periphery of the second wheel arbor. The stop mechanism, on the other hand, may consist of a mechanical means by which a limiting member is engaged with the gear train when a crown is drawn out or a magnetic means which magnetically locks the rotor member of the motor when the time piece is adjusted.
Such conventional mechanisms for preventing the transmission of reverse motion, however, presents several problems. For example, such mechanical means require a complex lever mechanism in order to properly actuate the limiting member and the magnetic means presents many difficulties in adjusting this slipping force of the above described slip mechanism.